1. Field of the Invention
The present invention relates to a high pressure hydraulic pump apparatus, and more particularly, to a plunger pump apparatus which is equally called as a hydraulic booster.
2. Related Background Art
Where a high pressure liquid is used for the cutting of works, the pressurization within pressure vessels or the like, high pressure hydraulic pump apparatus, based on the Pascal's principle and called as hydraulic booster pumps, are used widely as high pressure liquid supply source. The hydraulic booster pump produces a high delivery pressure by increasing an inlet pressure in inverse proportion to the pressure receiving area ratio of a plunger piston. Known types of hydraulic booster pumps are roughly classified into single-acting boosters adapted to intermittently deliver a high pressure liquid of a given flow rate from the outlet for every stroke and double-acting boosters comprising a pair of single-acting boosters interconnected via check valves and directional control valves to deliver a high pressure liquid of a continuous flow in time from the outlet.
A variety of mechanisms are heretofore known for hydraulically driving the plunger of a hydraulic booster. In the case of the hydraulic booster of a free piston type, for example, the interior of the pressure cylinder is divided into a processing chamber and a pressurizing chamber by the free piston and a liquid to be processed, is introduced to fill the processing chamber and pressurized by the movement of the free piston caused by the hydraulic oil introduced into the pressurizing chamber. Such a pressure cylinder is connected in parallel with a number of the similar pressure cylinders through valves and a phase difference in operation is provided for the free pistons of the respective cylinders, thereby attaining an efficient pressurized processing.
While this free piston-type hydraulic booster is advantageous in that during the operation of the free piston practically no pressure difference is caused between its chambers on the both sides thus tending to reduce the wear of the packing for sealing the clearance between the free piston and cylinder bore, it has been said to be unsuited in applications involving, for example, the pressure treatment of such beverages and comestibles as jam, fruit juice and wine or medicine due to the danger of the liquid to be processed in the processing chamber being contaminated by the actuating hydraulic oil within the pressurizing chamber.
As hydraulic high pressure pump apparatus for pressurization processing such beverages and comestibles, medicine or the like by a high pressure liquid, electrically-operated hydraulic boosters adapted for operating the plunger pump by a driving mechanism which is completely free of the danger of the liquid to be processed being contaminated by an actuating hydraulic oil, i.e., an electrically-operated motor have been frequently used.
However, the conventional electrically-operated hydraulic booster requires a separate rotary pump for supplying a liquid to be processed into the pressurizing chamber of the main pump. The volume of the rotary pump must be selected with some allowance in consideration of variations in the amount of liquid supplied into the pressurizing chamber of the main plunger pump. The provision of the rotary pump complicates the construction of the booster apparatus on the whole. Also, the liquid to be processed is caused to change in quality during its circulation within the rotary pump. Particularly, if bubbles are allowed to enter into the liquid to be processed prior to its pressurization in the pressurizing chamber of the main plunger pump, a long period of time is required before the liquid to be processed attains the target pressure owing to its pressurization by the plunger pump and thus the work efficiency of the pressurization is deteriorated. In addition, the occurrence of a seal leakage problem of the booster due to the connection of the rotary pump is apprehended.
On the other hand, in the case of the conventional double-action booster the hydraulic system is a single-stage pressurization system so that a sufficiently high delivery pressure cannot be obtained unless the shaft output of the drive motor is increased. In particular, while the use of a higher pressure is desired in the field of the pressurized processing of food products, the use of a high-power drive motor inevitably increases the cost and also it gives rise to the problem of increasing the size of the apparatus on the whole. In addition, the pump driving power must be increased in order to ensure a higher pressure for the delivery pressure performance of the booster. For this purpose, it is necessary to increase the diameter of the screw shaft of the ball screw unit which drives the plunger by converting the rotation output of the motor into a linear reciprocating motion. However, if the ball screw shaft is increased in diameter, the weight of the apparatus is necessarily increased and moreover the load bearing ability is not increased in proportion to the increase in weight with the resulting deterioration of the energy efficiency. Further, irrespective of the single-action booster and the double-action booster, the conventional electrically-operated booster is designed so that even if the load pressure reaches near a preset value and a situation arises in which it is sufficient even if the amount of delivery required for the pressurization of the load is less than the amount of delivery per stroke length of the plunger, the plunger is still caused to reciprocate at the constant stroke length and thus it is wasteful of the power consumption of the drive motor.